The present invention relates generally to a control application for a heating system. More specifically, the present invention relates to a method and apparatus for overriding the base controls of a heating system to provide heat from an auxiliary heat source.
Typically, heating systems have two independent heaters to provide heat to regulate the temperature of an interior space, such as a home. The first heater is a heat pump, and the second heater is an auxiliary heater. The auxiliary heater typically provides electrical resistance or fossil fuel heating. The electrical resistance heat may be in the form of electrically resistive wires positioned in a plenum of the heating system that generates heat in response to passing current through the wires. Air circulated past the heated wires in the plenum is likewise heated and circulated through the home. Alternately, the auxiliary heater may be in the form of electrical resistance baseboard heaters that are positioned throughout the home. The fossil fuel auxiliary heater receives and burns natural gas, oil or other fuel to provide heating to air in a plenum in the heating system that is circulated through the home. Additionally, the auxiliary heaters can be designed to provide two or more heating capacities, also commonly referred to as stages.
A heat pump's capacity to provide heat to a home decreases as the outside ambient temperature decreases. When the outside temperature is less than some preselected outdoor ambient temperature, typically referred to as the application balance point, auxiliary heat must be used with or in place of the heat pump to adequately heat the home. Additionally, when the outside temperature is less than a second preselected outdoor ambient temperature, heat pumps are a more expensive heating method than the auxiliary heater. This second preselected temperature is typically referred to as the economic balance point. This second preselected temperature depends on many factors including the efficiency of the heat pump, the type and efficiency of the auxiliary heater, the cost of electricity to operate the heat pump and the cost of fuel/electricity being used by the auxiliary heater. Ideally, the balance point used by the heating system is selected to be the higher of the application balance point and the economic balance point.
Depending upon the particular heat pump configuration, the heating system balance point can range considerably, from about 0° F. to about 45° F., for example. That is, if the heating system balance point is set considerably less than 32° F. and a problem occurs with the heat pump so that the heat pump cannot heat the home, there is the potential for significant damage to the home, such as from water pipes freezing. For example, if the heating system balance point temperature is set to 0° F. and the outdoor ambient temperature is 10° F., typical heating controls will not permit the auxiliary heater to operate because the outdoor ambient temperature is greater than the balance point temperature. If the heat pump malfunctions for any reason, i.e., failed power connection, internal compressor damage, etc., the home will not be heated. If the outside ambient temperature remains greater than the balance point temperature yet less than 32° F. for a sufficient period of time, pipe freezing may occur, especially if the homeowner is away during this period of time and unable to intervene.
What is needed is a method or apparatus for use with heating systems that can override the control system when the indoor room temperature is not being maintained as required, and the auxiliary heat is being prevented from operating by the balance point setting.